The present invention relates to a tuner device for a television receiver and, more particularly, to a circuit for selection of the television channel it is desired to receive, and to a conversion circuit for converting the signal received, from the frequency of the selected channel to the fixed intermediate frequency at which the signal amplification circuits operate. The selection and conversion circuits together are generally known as a "tuner."
There are many types of "tuners" on the market which differ from each other with regard to the arrangement of the circuits, but all have in common the complexity of the construction, particularly with respect to the assembly of the components and the calibration of the finished circuit.
Moreover, it is necessary to bear in mind that the circuits in question deal with signals the frequencies of which may lie between 48 MHz of the lowest channel of the VHF band and 855 MHz of the highest UHF channel. At these frequencies the influence of component position or layout of components on the behavior of the circuits are no longer negligible. In fact, at high frequencies, the connections between the various separate components themselves present impedance values which cannot be neglected in the design of the circuit and nor can the parasitic capacitance of each circuit element. In addition, the values of these distributed elements also vary with the geometry of the circuits, therefore rendering their a priori determination difficult, and this also makes the repeatability of the values from one circuit to another difficult.
For this reason, at the design stage, it is necessary to allow an adequate margin on some component values to permit calibration of the finished circuits in order to obtain proper operation since, due to tolerances on the circuit components themselves, the finished circuit may well need to undergo considerable adjustment by way of calibration before it functions properly.
In order to reduce this effect, many designers have tended to reduce the length of the connections between individual components by mounting them very close to one another on a printed circuit board. However, this leads to other difficulties since the assembly of the individual components onto the board involves very delicate operations because of the proximity of the components to one another.